Fuel regulator for aircraft carburetors



May 23, 1944. s UDALE 2,349,775

. FUEL REGULATOR FOR AIRCRAFT CARBURE'I'ORS Filed Jan. 19, 1943 Patented May 23, 1944 FUEL REGULATOR FOR AIRCRAFT CARBURETORS Stanley M. Udale, Detroit, Mich., assignor to George M. Holley and Earl Holley Application January 19, 1942. Serial No. 472,909

2 Claims.

This application is in part asubstitution for application filed July 23, 1940, Serial No. 346,973.

The object of this invention is to semi-automatically control the mixture ratio at any desired figure, so that if the pilot manually selects any given mixture ratio, the device will automatically change to and hold the mixture ratio at that desired figure.

In said drawing:

The figure shows diagrammatically the application of the device to a well known airplane carburetor. i

In the figure I is the air entrance; II is a streamlined bridge in the air entrance forming an annular venturi passage. The pilot tubes l2 and 13 are arranged so that they transmit pressures, the diiference between which will vary with the velocity squared times the density of the air. The pilot tube l2 facing upstream communicates with the chamber I4. The pilot tube 13 facing downstream communicates with the chamber IS. A diaphragm l6 forms the upper wall of the air chamber IS. The diaphragm l1 forms the lower wall of the air chamber M.) A

fuel chamber IB is located above the diaphragm iii. A fuel chamber I9 is located below the diaphragm l1. A rod 1| connects the two diaphragms l6, and I1 together. i

The fuel enters through the pipe 20 into the chamber l9, flows through the venturi 2| to the fuel outlet 22, whence it flows through the pipe 23 to the fuel entrance 24 to the diaphragm chamber 25. It flows through the outlet 26 past the needle 21 down the passage 28 through the nozzle 29 whence it discharges into the variable venturi formed between the streamlined central portion 30 and the streamlined throttles 3| and 32 which are connected together by the gears 33 and 34 in a well known manner.

A lever 35 is mounted on the throttle 32 and is also connected to the lever 36 which is in its turn connected to the needle 21 so that as the throttles 3|, 32 are opened, the needle 21 is also opened. The throttle 3| has an opening 31 located in the throat of the variable venturi. The vacuum is thus transmitted through the restriction 38 to the passage 33 which communicates with the chamber 40 which is connected through the passage 4| with the chamber 42. The chamber 40 is bounded on its left hand side by the diaphragm 43. The chamber 42 is bounded on its right hand side by the diaphragm 44. The fuel chamber 25 is therefore located between the diaphragms 43 and 44. These diaphragms are connected through the usual mechanism with the fuel inlet valves 45 and 46. A metering valve 41 controls the admission of air from a passage 1! connected to an annular chamber 12 (vented to the air entrance) to the passage 39. Hence, the movement of the valve 41 will regulate the flow of fuel directly, indirectly therefore, it controls the mixture ratio. The diaphragm 11 carries a movable contact 48 which engages with the end of a bi-metallic strip 49 which is designed to deflect upwardly when heated. This bimetallic strip 49 is surrounded by a heating coil connected through the conductor 50 with the storage battery 5|. The contact 48 is connected through the conductor 52 with the heating coil 53 which surrounds the oi-metallic strip 54 which is designed to deflect upwardly when heated and is mounted in the pin 55 which is rigidly mounted in the wall of the intake passage 10. To correct for altitude well known means are used namely, a pressure responsive element 6|, a valve 60, an adjustable element 62 and a bypass 63. The bypass 69 if unrestricted would cause the chambers l4 and I5 to be in equilibrium.

In order to vary the mixture ratio, a cam 56 is provided operated by lever 51. This cam engages with a needle 58 which varies the size of the throat of the venturi 2|.

Operation The thermostatic element 54 is designed so as to move clockwise that is to say, upwardly under the influence of the heating current in the coil 53. The valve 41 therefore descends and opens up the passage when heating current ceases to flow around the coil 53. This occurs when the contact is open between 48 and the end of the thermostatic bi-metallic element 49. This causes an increase in flow of fuel and the mixture ratio becomes richer. This increase in fuel flow through the venturi 2| causes an increase in the depression in the chamber It. This causes the diaphragm is to, rise. This causes the contact 48 to engage, therefore the current once more flows around heatingcoil 53. The thermostatic element 54 thereupon heats up and the valve 41 rises and the flow of fuel is thus reduced. Equilibrium is therefore reached determined by the size of the venturi 2| relative to the size of the annular air venturi into which the pilot tubes l2 and I 3 project. When this mixture ratio is to be varied, the lever 51 is moved, When it is moved downwardly, the needle58 rises and restricts the throat of the venturi 2|. When this happens, a smaller flow of fuel will balance a given airflow; in other words, the valve 41-will be an equilibrium when'the mixture ratio is lean and of course, the reverse happens, when the needle valve 58 moves in the reverse direction.

What I claim is:

1. A carburetor having an air metering venturi of fixed throat area, a chamber located out of the airstream and connected to the throat of said venturi, a second chamber also located out of the airstream and connected to a portion of the airstreamhaving a relatively low air flow velocity, a fuel venturi of vfixed size, a chamber located out of the fuel stream and connected to the throat of said fuel venturi, a second chamber also located out of the fuel stream and connected to aportion of the fuel stream having a relatively low rate of fuel flow, means including two diaphragms connected together and responsive to the pressure difierences in said four chambers and adapted to balance the pressure drop in the throat of the fuel venturi against the pressure drop created in the throat of the air venturi, an electric circuit, an electrical contact carried by one of the diaphragms and 10- cated in said circuit, a heating coil in said circuit, a heat responsive element associated with said heating coll, an electric contact mounted on said element and adapted to engage with the contact on the diaphragm, a second electrical heating coil, 9. second heat responsive element associated with the secondheating coil, 9. fuel flow control valve connected to the second heat responsive element, the second electrical heating coil being in circuit with the first electricalheating coil and with the two contacts whereby when the ratio of fuel flow to air flow increases as measured by the unbalanced fuel and air pressure acting upon the said diaphragms, the second heat responsive element is heated and deformed so as to move the fuel flow control valve in the direction which will cause a reduction in fuel flow.

2. A carburetor as set forth in claim 1 in which there are means for varying the area of the throat of the fuel venturi for the purpose described.

STANLEY M. UDALE. 

